Pulmonary embolism is a common disorder accompanied by a significant morbidity and mortality. Thromboembolism may either be acute through activation of the blood clotting system and disseminated intravascular coagulation, or occur at a later stage through the formation of thrombi in the pulmonary vessels or formation in the venous circulation with subsequent embolisation to the lung. The mortality rate for patients with pulmonary embolism is higher than in patients with acute myocardial infarction, exceeding 10% at 30 days and 16% at 3 months according to various studies. It has been estimated that pulmonary embolism accounts for 10% of all deaths in hospitals, and is a major contributing factor in a further 10%.
Pregnant women, and in particular women undergoing caesarean section, cancer patients, trauma victims, and patients undergoing surgery (e.g., orthopaedic surgery) are at risk. Further risk groups include individuals confined to bed rest or other types of confinement or restriction in the movement of the body of limbs, both during medical treatment or recovery from such treatment, or during transportation, (e.g., travel by air). Further risk groups include patients with infections and those suffering from diseases or undergoing pharmaceutical treatments that can disturb the blood clotting system or the system for resolution of blood clots.
Deep venous thrombosis (DVT) with the attendant risk of pulmonary embolism and post phlebitic syndrome is a frequent complication in older patients who have undergone surgery, suffered trauma or who have serious illness such as malignancy or sepsis. In any category, patients who are 40 years of age or older are considered to be at greatest risk. Also, the longer the period of immobilization the greater the risk of DVT. Other factors that have been reported to contribute to development of DVT are obesity, prior history of DVT, and smoking. Heart failure patients have increased risk of DVT on the order of three times that of the general population.